A smart magnetometer which includes at least one cantilevered magnetostrictive/optical fiber structural bonded composite in a vibrationally isolated housing allowing an optical signal to be transmitted and detected from one optical fiber to another such that fluctuations of the surrounding magnetic field H will cause fluctuating mechanical torque on the composite magnetostrictive beam which will be applied to the bonded cantilevered optical fiber to deflect or misalign and cause modulation of the optical signal transmitted between the two fibers. This modulation can be calibrated to the dynamic variation of strength of a neighboring magnetic field to a precision and sensitivity of less than 1 fT and 1 fT/sqrtHz. The system is smart to selectively filter out any neighboring magnetic field with average strength smaller or greater than a certain critical value. The system is also smart enough to switch from one magnetic field average strength and/or direction to another with different average strength and/or direction.

1. Field of the Invention
This invention relates to fiber optic magnetometers that are smart enough to selectively filter out magnetic fields and variations there of and easily have an a accuracy of less than 1 fT and sensitivities of less than 1 fT/sqrtHz and more particularly to fiber optic magnetic sensors of controllable precision.
2. Prior Art
The prior art is replete with many optical fiber sensors and different variations in Fabry-Perot, Mach-Zehnder modulators or Kerr effect or other optical effect-based magnetic sensors including squid type magnetometer. All of current devices have one or more of the following disadvantages: excessive bulk, slow response, require liquid helium cryogenic temperatures and poor mechanical reliability. Here below we present some typical examples but by no means exhaustive:
It is appropriate to mention some prior art related to the field of the present invention.
U.S. Pat. No. 4,588,947, to Ketchen, issued May 1986 discusses a miniature, fully integrated susceptometer capable of measuring the magnetic properties of very small samples ( less than 10 xcexcm) is described which is fabricated by thin film lithography on a single chip. The susceptometer is comprised of a dc SQUID including two series wired pick-up loops into which a sample to be measured can be placed. A field coil is provided which includes a separate single turn around each of the SQUID pick-up loops. The SQUID pick-up loops and the surrounding field coil turns are both located over a hole in a superconducting ground plane.
Daalmans in U.S. Pat. No. 4,801,882, issued January 1989 discusses a SQUID magnetometer, which can be fabricated by thin-film technology and used for apparatus for measuring weak magnetic fields. It contains a d-c SQUID with a SQUID loop surrounding the effective area of a coupling hole as well as a superconducting flux transformer with a gradiometer coil and a coupling coil surrounding the coupling hole thereby to achieve an effective inductive coupling of a measuring signal into the SQUID. To this end, the invention provides a separate superconducting surface with the coupling hole, to which the coupling coil and or the SQUID loop is/are assigned.
Hubbell in U.S. Pat. No. 6,005,380, issued December 1999 describes a magnetic field sensor, which can be used as an active antenna is disclosed that is capable of small size, ultra wide band operation, and high efficiency. The sensor includes a multiplicity of magnetic field transducers, e.g., superconducting quantum interference devices (SQUIDs) or Mach-Zehnder modulators that are electrically coupled in a serial array. Dummy SQUIDs may be used about the perimeter of the SQUID array, and electrically coupled to the active SQUIDs for eliminating edge effects that otherwise would occur because of the currents that flow within the SQUIDs. Either a magnetic flux transformer, which collects the magnetic flux and distributes the flux to the transducers or a feedback assembly (bias circuit) or both may be used for increasing the sensitivity and linear dynamic range of the antenna.
Bowman, et. al., in U.S. Pat. No. 3,750,017 issued July 1973 discuss an electromagnetic field measuring device is disclosed having a response which is essentially independent of the physical orientation of the device in the electromagnetic field. Further, the response of the device is essentially independent of the polarization of the field or of the presence of reactive field components or multipath interference. A set of three antennas disposed in a mutually orthogonal relationship with an essentially common center is provided, the antennas being adapted to be placed in an electromagnetic field to be measured. Sensing means, in the form of diodes for example, are associated with each antenna for deriving a signal therefrom. In the preferred embodiment, such antennas may take the form of dipoles, and diodes are contemplated to be connected between the dipole legs. The derived signals so produced are removed from the antennas in a fashion wherein no substantial perturbation of the field to be measured occurs and without substantially affecting the electrical characteristics of the antenna set. In a preferred embodiment, a high-resistance transmission line is provided. Subsequently, the derived and removed signals are combined and processed so as to generate a measurement reading.
Odawara, et. al., in U.S. Pat. No. 5,280,242 issued February 1991, discuss an apparatus for detecting a fine magnetic field comprises a DC SQUID, which detects and converts a magnetic field to an electrical signal. A flux locked looped circuit drives the DC SQUID. The flux locked loop circuit includes an amplifier for amplifying the electrical signal. A phase detector modulates the amplified electrical signal and an integration circuit outputs a voltage signal corresponding to the detected magnetic field. An oscillator coupled to the phase detector supplies a demodulation frequency signal. A modulator including a first voltage-to-current converter and a second voltage-to-current converter is coupled with the integration circuit and the oscillator for supplying a modulation signal to the DC SQUID. The modulator further includes an external input terminal and a feedback modulation change-over circuit for changing an internal feedback signal to an external test signal inputted to the external input terminal. A bias source having a third voltage-to-current converter is coupled to the DC SQUID and supplies a bias signal. The bias source also includes an external input terminal and a change-over circuit for changing an internal bias. signal to an external test signal inputted to the second external input terminal.
Crum, et. al., in U.S. Pat. No. 4,793,355 issued December 1988, discuss a biomagnetometer for measuring magnetic fields produced by the body and an electromagnetic location measurement and recording system for automatically determining the location of the portion of the body from which the magnetic signals are being gathered. The electromagnetic location recording system permits establishing a real time body frame of reference with respect to the biomagnetometer, so that biomagnetic signals can be correlated directly with body location and structure. The electromagnetic location recording system may be operated continuously at radiation wavelengths, which do not interfere with the taking of data, or intermittently with the taking of biomagnetic data, to avoid interference with the measured values of the biomagnetic data. The elements of the electromagnetic location recording system have substantially no residual magnetism when the location recording system is not operating, as the biomagnetic signals are typically so small that even normal residual magnetism might be erroneously recorded as a biomagnetic signal.
Johnson, et. al., in U.S. Pat. No. 5,444,373 issued August 1995, discuss a biomagnetometer comprising an array of biomagnetic sensors, the array comprising a first plurality of magnetic field pickup coils, and a second plurality of detectors, each of which receives a pickup coil output from a pickup coil. There is a third plurality of signal processors, each of which receives an output from a detector, the third plurality of signal processors being fewer in number than the first plurality of pickup coils. The biomagnetometer further includes a selector that selects a subset of pickup coils, equal in number to the third plurality of signal processors, from the first plurality of pickup coils for signal processing by the signal processors. This biomagnetometer permits the placement of a very large array of relatively inexpensive pickup coils adjacent to a subject, and then processing information from subsets of that large array selected to optimize the gathering of data, while maintaining the cost of the signal processing electronics at a more economical level.
Robinson, et. al., in U.S. Pat. No. 4,977,896 issued December 1990, discuss how signals produced by brain activity are measured by each sensor of an array of magnetic and/or electrical sensors external to but proximate to the head (or other portion of the body) of a subject. The measurements obtained simultaneously from all of the sensors are combined in a manner to permit selective measurement of the electrical activity from a specified location within the body, or alternatively, to permit the location in the body producing a particular type of response to be identified. The instantaneous measurement of each sensor is scaled by a weighting coefficient for that sensor, and the products added over all of the sensors. The weighting coefficients are calculated from a mathematical model of the brain that includes information on the shape of the potential source, the extent or type of source activity, the electrical and magnetic properties of the media, and the locations and orientations of the sources and the sensors.
Tsukada, et. al., in U.S. Pat. issued May 2001, discuss a biomagnetic field measuring apparatus that has a plurality of flux meters disposed externally of a living body and each including a superconducting quantum interference device (SQUID) for detecting a biomagnetic field generated from the living body, the plurality of flux meters being operative to detect a temporal change of a component of the biomagnetic field in a first direction which is normal to the surface of the living body, an operation processor for performing computation for determining a temporal change of a value proportional to a root of square sum of differential values of the first-direction magnetic field component in second and third directions which cross the first direction and computation for integrating the temporal change of the value over a predetermined interval to determine an integral value, and a display for displaying the determined integral value. Distribution of magnetic fields generated from the heart is determined with a small number of flux meters. Based on the above description it can be observed that this device is SQUID based and therefore is different from our presented invention.
Kuc, et. al., in U.S. Pat. No. 5,594,849 issued January 1997, discuss a method and apparatus for performing biomagnetic imaging to determine the location and intensity of current sources within a subject, which includes a sensor unit for sensing the magnetic field within the subject and for providing sensing signals. A signal processor defines a grid having multiple grid points and performs inverse estimation to determine the distribution of current sources on the defined grid based on the sensing signals. The signal processor then modifies the grid to improve the resolution of the current sources distributed on the grid. A control unit controls the operation of the signal processor and processes image data to provide magnified and non-magnified displays on a display unit. The biomagnetic imaging method and apparatus can be combined with a system for providing magnetic resonance imaging data so as to produce a superimposed display including an MRI image and a biomagnetic image.
U.S. Pat. No. 4,368,430 by Dale, et al. Jan. 11, 1983 entitled xe2x80x9cFiber optic magnetic sensorsxe2x80x9d which basically discussed A magnetometer which includes a pair of spaced apart optical fibers at least one of which comprises a cantilevered beam having a dipolar magnet thereon such that fluctuations of the magnetic H field will cause fluctuating mechanical torque on the magnet which will be applied to the cantilevered optical fiber to deflect same and occasion modulation of an optical signal transmitted between the two fibers.
U.S. Pat. No. 6,304,083 by Owens issued Oct. 16, 2001 entitled xe2x80x9cMagnetic field sensor with colossal magneto-resistive material contained within the coil of an oscillatorxe2x80x9d which discusses Sensors, systems and methods for measuring magnetic field strengths in both AC and DC magnetic fields by using CMR material in tunable, radio-frequency LC oscillators are disclosed.
U.S. Pat. No. 5,958,154 by O""Handley, et al. Sept. 28, 1999, entitled xe2x80x9cHigh-strain, magnetic field-controlled actuator materialsxe2x80x9d, which discusses Magnetically-controlled actuator materials are provided that produce large actuation stroke, that exhibit fast actuation response time and corresponding high-frequency operation, and that enable efficient actuation energy conversion at convenient operating temperatures. The actuator materials exhibit an austenitic crystal structure above a characteristic phase transformation temperature and exhibit a martensitic twinned crystal structure below the phase transformation temperature. One actuator material provided by the invention is an alloy composition that can be defined generally as (Ni.sub.a Fe.sub.b Co.sub.c).sub.65xe2x88x92xxe2x88x92y (Mn.sub.d Fe.sub.e Co.sub.f).sub.20+x (Ga.sub.g Si.sub.h Al.sub.i).sub.15+y, where x is between about 3 atomic % and about 15 atomic % and y is between about 3 atomic % and about 12 atomic %, and where a+b+c=1, where d+e+f=1, and g+h+i=1. The actuator material is characterized by a magnetocrystalline anisotropy energy that is sufficient for enabling motion of twin boundaries of the martensitic twinned crystal structure in response to application of a magnetic field to the martensitic twinned crystal structure. This enables the material to produce an actuation stroke in response to the magnetic field. Based on this actuation mechanism, the actuator materials of the invention overcome the thermal, stroke, and frequency response limitations typically associated with actuator materials, and enable a class of actuators with large stroke and high speed at convenient temperature.
U.S. Pat. No. 5,776,359 to Schultz, et al. Jul. 7, 1998, entitled xe2x80x9cGiant magnetoresistive cobalt oxide compoundsxe2x80x9d, which discusses Methods and apparatus for the preparation and use of a substrate having an array of diverse materials in predefined regions thereon. A substrate having an array of diverse materials thereon is generally prepared by delivering components of materials to predefined regions on a substrate, and simultaneously reacting the components to form at least two materials. Materials, which can be prepared using the methods and apparatus of the present invention, include, for example, covalent network solids, ionic solids and molecular solids. More particularly, materials which can be prepared using the methods and apparatus of the present invention include, for example, inorganic materials, intermetallic materials, metal alloys, ceramic materials, organic materials, organometallic materials, non-biologicalorganic polymers, composite materials (e.g., inorganic composites, organic composites, or combinations thereof), etc. Once prepared, these materials can be screened for useful properties including, for example, electrical, thermal, mechanical, morphological, optical, magnetic, chemical, or other properties. Thus, the present invention provides methods for the parallel synthesis and analysis of novel materials having useful properties.
U.S. Pat. No. 5,446,377 to Mohri, et al. issued Aug. 29, 1995, entitled xe2x80x9cMagnetic detector using Matteucci effectxe2x80x9d which discusses A magnetic detector for detecting a magnetism present in the vicinity of or close to a magnetic wire circumferentially magnetized therein and an electromagnet for generating an A.C. magnetic field on the basis of the magnitude of a Matteucci-effect voltage developed across the magnetic wire when the electromagnet approaches the magnetic wire. A coordinate input device for detecting proximity between the electromagnet and an array of a plurality of such magnetic wires arranged in X and Y directions when the electromagnet approaches the array. A magnetic image sensor for detecting an intensity distribution of a static magnetic field to be detected and present along a longitudinal direction of the wire on the basis of a detection voltage of the wire when a plurality of such electromagnets arranged along the longitudinal direction of the wire are sequentially excited one after another.
U.S. Pat. No. 5,103,174 to Wandass, et al. issued Apr. 7, 1992, entitled Magnetic field sensor and device for determining the magnetostriction of a material based on a tunneling tip detector and methods of using samexe2x80x9d, which discusses a tunneling tip piezo incorporated into various devices for measuring effect of changes in environmental conditions (i.e., temperature, pressure, magnetic and electrical fields, etc) upon a material by sensing minute changes in the dimensions of the surface. The devices may be used to detect changes in environmental conditions or to determine physical properties of a material.
U.S. Pat. No. 5,073,858 to Mills, issued Dec. 17, 1991, entitled xe2x80x9cMagnetic susceptibility imaging (MSI),xe2x80x9d discusses Magnetic Susceptibility Imaging (MSI) comprises a generator to magnetize the tissue to be imaged, such as a first Helmholtz coil, which produces a high-strength external magnetic field to which unpaired electrons of paramagnetic molecules of tissue, which includes primarily deoxyhemoglobin and oxygen, couple in a positive sense, and to which orbital electrons of diamagnetic molecules of tissue, such as proteins and water, couple in a negative sense to produce a secondary magnetic field. The imaging system further comprises a nullifier to null the external magnetizing field, such as a second Helmholtz coil which, for example, confines the flux of both of the coils to a single plane such that the component of the secondary field perpendicular to this plane is the only field with a nonzero component. The secondary field component is detected by a detector, such as an array of Hall voltage detectors. The detection is performed over a sample space, and the signals recorded from the secondary field are used to reconstruct the magnetic susceptibility function of the body using the reconstruction processor of the present invention, such as a Fourier Transform Algorithm processor.
U.S. Pat. No. 5,039,943 to Weber, et al., issued Aug. 13, 1991, entitled xe2x80x9cMagnetostrictive magnetometer,xe2x80x9d teaches A magnetometer which employs a rod of magnetostrictive material comprising a ternary alloy of dysprosium, terbium and iron wherein the grains of the material have their common principal axes substantially pointed along the axis of the rod. Means are provided for compressively stressing the rod in order to enhance the magnetostrictive response thereof. A laser source and photosensor are associated with a free end of the rod to function as an external cavity laser sensor. A DC magnetic bias is required for the magnetostrictive rod in order to operate in the sensitive range of the magnetostrictive characteristics of the rod. In a portable implementation of the device, the DC bias is provided by means of permanent magnets, preferably rare earth magnets, in order to provide the high bias fields compatible with high sensitivity of the material in a miniaturized portable device.
U.S. Pat. No. 5,038,103 to Scarzello, et al., issued Aug. 6, 1991, entitled xe2x80x9cOptical fiber magnetometer,xe2x80x9d discusses An optical fiber magnetometer having omnidirectional capability is disclosed herein for measuring a total magnetic field independent of its physical orientation or the direction of the field or fields. A relatively long optical fiber defining a sensing arm for exposure to a magnetic field is wound in the form of a spheroid (like rubber bands on a golf ball or yarn threads on a baseball) to provide optical path lengths of substantially the same total length in every direction through the spheroid winding. The plane of polarization of light transmitted through the optical fiber winding is caused to rotate (Faraday effect) when the fiber or components thereof is exposed parallel to a magnetic field. The extent of plane rotation is determined, inter alia, by the total magnetic field passing through the spheroid winding.
U.S. Pat. No. 5,015,953 to Ferguson, et al., issued May 14, 1991, entitled xe2x80x9cMagnetometer for detecting DC magnetic field variations,xe2x80x9d teaches A magnetometer for detecting variations in a DC magnetic field. The magnetometer includes a magnetic field variation sensitive device that resonates at a characteristic resonant frequency by converting energy stored therein as a result of being excited by electromagnetic radiation at twice the resonant frequency when biased by a DC magnetic bias field within a predetermined field intensity range in which the amplitude of the resonance varies with variations of the field intensity. The magnetometer further includes an excitation circuit for exciting the device to resonate at the characteristic resonant frequency at an amplitude level that remains constant when the DC magnetic bias field intensity does not vary and is within the predetermined field intensity range; a DC voltage source within the excitation circuit for biasing the device with a DC magnetic bias field that is within the predetermined field intensity range; and a sensing instrument for sensing the amplitude of the resonance of the device at the characteristic resonant frequency. A variation in the amplitude of the resonance sensed by the sensing instrument indicates a variation in the intensity of the DC magnetic bias field. The magnetometer is utilized in a variety of different systems, including a system for actuating an output instrument, such as a traffic signal controller, in response to a predetermined threshold variation in a DC magnetic bias field, such as occurs when a motor vehicle moves into the vicinity of the magnetometer; a system for probing for materials whose presence affects the intensity of a DC magnetic bias field, such as buried pipes or ferromagnetic mineral deposits; a system for communicating in the low frequency range of the electromagnetic spectrum; and a system for guiding a probe with respect to the location of an object whose presence causes a variation in the intensity of a magnetic bias field.
U.S. Pat. No. 4,951,674 to Zanakis, et al., issued Aug, 28, 1990, entitled xe2x80x9cBiomagnetic analytical system using fiber-optic magnetic sensors,xe2x80x9d discusses A biomagnetic analytical system for sensing and indicating minute magnetic fields emanating from the brain or from any other tissue region of interest in a subject under study. The system includes a magnetic pick-up device constituted by an array of fiber-optic magnetic sensors mounted at positions distributed throughout the inner confines of a magnetic shield configured to conform generally to the head of the subject or whatever other body region is of interest. Each sensor yields a light beam whose phase or other parameter is modulated in accordance with the magnetic field emanating from the related site in the region. The modulated beam from each sensor is compared in an interferometer with a reference light beam to yield an output signal that is a function of the magnetic field being emitted at the related site. The output signals from the interferometer are processed to provide a display or recording exhibiting the pattern or map of magnetic fields resulting from emanations at the multitude of sites encompassed by the region.
U.S. Pat. No. 4,918,371 to Bobb, issued Apr. 17, 1990, entitled xe2x80x9cFiber optic magnetometers for multiple order gradiometers,xe2x80x9d teaches Magnetometers disposed as magnetostrictive segments on optical fiber element are incorporated in multiple order gradiometers to reduce the size, weight and cost thereof. in the preferred embodiments, such reductions are greatly enhanced by consolidating a plurality of magnetometers on individual optical fiber elements, which also serves to decrease the number of devices associated with the magnetometers in the multiple order gradiometers.
U.S. Pat. No. 4,769,599 to Mermelstein, issued Sept. 6, 1988, entitled xe2x80x9cMagnetometer with magnetostrictive member of stress variable magnetic permeability,xe2x80x9d discusses A highly sensitive magnetometer employs a magnetostrictive amorphous metal core in which a piezoelectric driver induces stress variations. In the presence of an external magnetic field, the magnetization of the magnetostrictive core varies in relation to the induced stress. The amplitude of the variations in magnetization is proportional to the strength of the external field and is sensed by a pick-up winding disposed around the magnetostrictive core. The dynamic range of the device is improved by employing a bucking field winding around the core to null out the magnetization of the core. In contrast to the inherent nonlinear characteristic of the conventional fluxgate magnetometer, the invention inherently provides a linear response to magnetic field strength.
U.S. Pat. No. 4,712,065 to Pitt, et al., issued Dec. 8, 1987, entitled xe2x80x9cMagnetic field sensors, in particular optical fiber magnetometers,xe2x80x9d teaches In a fiber optic interferometric magnetic sensor or magnetic gradient detector a magnetic bias field is applied to a magnetically sensitized portion of an optical fiber by means which are driven by optical power whereby a completely passive sensor head arrangement may be achieved. In a magnetic gradient detector optical power from a high power laser (34) may be supplied via an optical fiber (35) to illuminate a solar cell 27 to whose electrical output terminals solenoids (25,26) are connected. A portion of a respective optical fiber (21, 22), which is magnetically sensitized, by for example bonding to a strip of magnetostrictive material (23, 24), is disposed inside each solenoid (25, 26).
U.S. Pat. No. 4,675,522 to Arunkumar issued Jun. 23, 1987, entitled xe2x80x9cFiber optic magnetic field sensor,xe2x80x9d teaches The present invention provides an improved fiber optic magnetometer having particular application for use in environments having large magnetic field ranges and gradients, such as space based applications. The magnetometer includes a laser, which generates a coherent beam of light, which is split by a beam splitter into first and second beams. The first beam is passed through a single mode fiber optic having a short metallic conductor attached to it. This fiber is referred to as the xe2x80x9csensor armxe2x80x9d of the magnetometer. The second beam is passed through another single mode fiber, which is wrapped around a modulator that is coupled to a feedback circuit. This adjusts the magnetometer such that ambient system noise is filtered and the device is maintained at maximum sensitivity. The output of the two fibers is combined forming a Mach-Zehnder interferometer. A current I is passed through the conductor in the sensor arm. If this fiber is in the vicinity of a magnetic field, displacement of the current carrying conductor will cause the fiber to bow. The resulting stretching of the fiber increases the path length for the light beam traversing through the sensor arm. The subsequent phase change measured by the Mach-Zehnder is related to the force exerted by the magnetic field on the conductor. The direction in which the fiber bows is dependent upon the magnetic field direction. The present invention also discloses an improved modulator for maintaining the present invention at the point of optimum operation.
U.S. Pat. No. 4,587,487 to Zanzucchi, issued May 6, 1986, entitled xe2x80x9cOptical fiber magnetometer for measuring D.C. and low frequency fields,xe2x80x9d discusses An optical fiber magnetometer employing balanced magnetostrictive oscillations to measure D.C. and low frequency ambient magnetic fields. The magnetometer includes an optical fiber interferometer 18 having a laser beam input 10 for travel through first and second arms 14, 16 of the interferometer. First and second magnetostrictive rods 20, 22 forming a matched pair are coupled to the respective optical fibers in the first and second interferometer arms 14, 16. An applied oscillating magnetic field is applied to each of the rods 180 degree, out of phase. The D.C. or low magnetic field to be measured, when combined with each of the applied fields, induces a change in the path length of each of the interferometer arms. The difference in the change in path length of each of the interferometer arms is determined to develop a signal representative of the D.C. to low frequency ambient magnetic field.
U.S. Pat. No. 4,516,021 to Taylor, issued May 7, 1985, entitled xe2x80x9cFiber optic magnetic field sensor,xe2x80x9d teaches An optical fiber magnetometer utilizing, in one embodiment, a birefringment optical fiber in combination with a magnetostrictive block for inducing strains in the fiber in response to an applied magnetic field to thereby cause a change in the degree of birefringence of the fiber. This change in birefringence is measured by directing the light exiting the fiber through a conversion element such as a polarizer or a prism and then detecting the resulting intensity modulation in a photodetector. A variety of inventive features are set out in this disclosure including the use of spliced fibers with a 90 degree axis rotation to compensate for environmental effects, the use of a twisted fiber for gradient field sensing, and the rotation of the sensor fiber to eliminate low-frequency noise and to obtain a vector field and field gradient sensing capability.
U.S. Pat. No. 4,037,149 to Foner, issued Jul. 19, 1977, entitled xe2x80x9cMultiple mode magnetometers,xe2x80x9d discusses A magnetometer in which at least two modes of drive are employed in exciting sensor and/or sample so that the sensor provides an output indication of magnetic moment, which is a function of both drive modes. The drive modes may be periodic at specific driving frequencies, a periodic or may comprise a unidirectional portion of a mode. The output of the sensor contains components representative of the frequency or frequencies of the first mode modulated at the frequency or frequencies of the second mode. This sensor output is then analyzed to provide an indication of sample magnetic moment as a function of the frequency components of both modes of drive in order to eliminate contributions to the indicated magnetic moment from background signals or other perturbations, which may be present under, single mode operation. The multiple mode magnetometer is useful in several embodiments for production line applications, investigations of magnetic properties of inhomogeneous magnetic materials, as well as for general magnetic moment measurements. The concept of a multimode magnetometer also may be extended to include a multiplicity of modes.
U.S. Pat. No. 4,471,219 to Giallorenzi, issued Sept. 11, 1984, entitled xe2x80x9cAmplitude mode magnetic sensors,xe2x80x9d teaches A magnetic field sensor for detecting a magnetic field perturbation while nulling out variations in the signal caused by acoustic perturbations comprising a first and second optical fibers, an adjustable optical coupler for coupling light there between, a magnetic component attached to the optical coupler for exerting a mechanical force thereon proportional to a magnetic field perturbation to thereby change the degree of coupling between the fibers, and an optical detector for determining the amount of light actually being coupled between the fibers. As noted above, the system includes an acoustic circuit for nulling out the response in the detector signal due to acoustic perturbations. Two separate embodiments are disclosed. A first embodiment modulates the axial alignment of fibers in an end-to-end configuration by means of a magnetic material. A second embodiment modulates the evanescent coupling between the fibers disposed in parallel adjacency via a magnetostrictive material.
U.S. Pat. No. 4,656,421 to Ellis, et al., issued Apr. 7, 1987, entitled xe2x80x9cMagnetic field sensors,xe2x80x9d discusses A magnetic field sensor in the form of an element comprising two superimposed strips of material is described. The magnetostrictive constant along the longitudinal axis of one of the strips is greater than that of the other strip, the latter strip carrying at each end a post. In use of the sensor a single mode optical fiber is attached to the element via the posts such that the part of the fiber between the posts extends along a chord of the arc defined by the element. A variation in applied magnetic field in the plane containing the arc gives rise to a variation in the part of the fiber between the posts. Light passing through the fiber is thus phase shifted by an amount dependent on the value of the applied magnetic field.
U.S. Pat. No. 6,279,406 to Li, et al., issued Aug. 28, 2001, entitled xe2x80x9cPassive solid-state magnetic field sensors and applications therefore,xe2x80x9d teaches Passive solid-state magnetic sensors are based on the combination of magnetorestrictive materials and piezoelectric materials. Sensors have applications in rotor speed detection, magnetic field detection, read heads, and MRAM, for example.
U.S. Pat. No. 6,281,976 to Taylor, et al., issued Aug. 28, 2001, entitled Fiber optic fiber Fabry-Perot interferometer diaphragm sensor and method of measurement, A fiber optic fiber Fabry-Perot interferometer diaphragm sensor and method of measurement is provided. A fiber Fabry-Perot interferometer diaphragm sensor includes a base and a diaphragm with an optic fiber coupled under tension between the base and the diaphragm. A fiber Fabry-Perot interferometer element.(40) is contained within the optic fiber and operates to sense movement of the diaphragm. In a particular embodiment, the diaphragm moves in response to a pressure (P) applied to the diaphragm . In another embodiment, a proof mass is coupled to the diaphragm such that the diaphragm moves in response to an acceleration. In yet another embodiment, a magnetic body is coupled to the diaphragm such that the diaphragm moves in response to a magnetic field .
U.S. Pat. No. 5,982,174 to Wagreich, et al., issued Nov. 9, 1999, entitled xe2x80x9cExternal cavity fiber Fabry-Perot magnetometer,xe2x80x9d A magnetometer uses a material exhibiting the Faraday effect, in which the polarization of light transmitted through the material is changed in response to a magnetic field. When the material is placed in a Fabry-Perot cavity, multiple reflections of the light within the Fabry-Perot cavity increase the change in polarization and thus the sensitivity of the magnetometer. Other effects that alter the polarization of light can be employed instead.
U.S. Pat. No. 5,736,856 to Oliver, et al., issued Apr. 7, 1998, entitled xe2x80x9cMethod and apparatus for performing magnetic field measurements using magneto-optic Kerr effect sensors,xe2x80x9d teaches A sensor system includes a magneto-optic Kerr effect magnetic field sensing element and an optical system including a light source, at least one polarizer or polarizing element and a detector disposed about the sensing element. The sensing element is responsive to an external magnetic field. In one embodiment, the optical system and sensing element can be arranged to measure the strength of a magnetic field. In another embodiment the optical system and sensing element can be arranged to measure the rotational speed of rotating members.
U.S. Pat. No. 5,471,139 to Zadoff, issued Nov. 28, 1995, entitled xe2x80x9cFiber optic line magnetometer having thermal compensation,xe2x80x9d discusses A fiber optic line magnetometer is used in a railway block detection system for detecting the presence of a train, or a portion of a train, within a predetermined block. The fiber optic line magnetometer is positioned in the center of the tracks and runs parallel to the tracks for the entire length of the block. The fiber optic line magnetometer includes a sense arm and a reference arm, each of which includes a fiber optic cable for carrying a light originating from a signal source. Magnetostrictive elements connect to the fiber optic cable in the sense arm and change the light path length when external magnetic fields are applied thereto. The light exiting from the sense arm and the reference arm are compared, and in the event the fringe shifts in the compared light exceeds predetermined thresholds, a detection control signal is generated. Non-magnetostrictive elements, which are sized to have the same thermal temperature expansion characteristics as the magnetostrictive elements, are attached to the fiber optic cable of the reference arm.
U.S. Pat. No. 4,609,871 to Bobb, issued Sept. 2, 1986, entitled xe2x80x9cTemperature compensated optical fiber interferometric magnetometer,xe2x80x9d teaches Temperature compensation of an optical fiber interferometer is achieved by wrapping and bonding one fiber arm transversely about the length of a magnetostrictive rod which is sensitive only to the magnetic field component along its length. The other fiber arm is wrapped and bonded about two generally semicircular caps, attached to either end of therod, in a direction along the longitudinal axis of the rod.
U.S. Pat. No. 4,600,885 to Koo, et al., issued Jul. 15, 1986, entitled xe2x80x9cFiber optic magnetometer for detecting DC magnetic fields,xe2x80x9d teaches A fiber optic magnetometer for detecting DC magnetic fields includes a first optical fiber having a magnetostrictive jacket thereon which defines a sensing arm, and a second fiber defining a reference arm. An AC magnetic field of frequency xcfx890 and constant amplitude is imposed on the magnetostrictive jacket so as to cause a time varying optical path length change, having an xcfx890 component, in the sensing arm fiber. This induces a corresponding time varying phase shift, also having an xcfx890 component, in light transmitted through the sensing arm fiber, which is detected by a phase detector. The phase detector produces a signal proportional to the phase shift, this signal being passed to a lock-in amplifier set to amplify at xcfx890. The lock-in amplifier produces an output signal proportional to the amplitude of the xcfx890 component, wherein this amplitude is proportional to any DC magnetic fields to which the device is exposed.
U.S. Pat. No. 4,665,363 to Extance, et al., issued May 12,1987, entitled xe2x80x9cOptical fiber magnetic gradient detector,xe2x80x9d Two portions (B,C) of one arm of an optical fiber Mach-Zehnder interferometer are magnetically sensitized and each has applied thereto an a.c. bias fields at a respective different frequency (w.sub.1, w.sub.2). One portion (A) of the other arm of the interferometer is magnetically sensitized and has two a.c. bias fields applied thereto, each at one of the different frequencies (w.sub.1, w.sub.2). The fields for portion A and C are aligned with a first direction (x) whereas those for A and B are parallel, A and B being separated in a second direction (y). The detected output of the interferometer at frequency w.sub.1 is related to the magnetic gradient in the y direction, whereas the detected output at frequency w.sub.2 is related to the magnetic gradient in the x direction. Thus using two bias frequencies allows one interferometer to be used to detect two gradients.
Therefore it appears that based on the prior art just reported there are no identical devices existing in the prior art that are smart in the sense of the proposed invention. The proposed invention is neither SQUID-based nor based on any optical effects such as Fabry-Perot interferometery or other types of fiber optic interferometry.
Accordingly, it is an object of this invention to provide a smart and improved magnetic sensors that can selectively filter out magnetic fields or variations there of greater or smaller than a certain critical value.
Briefly, the said invention discusses a smart magnetometer which includes a cantilevered magnetostrictive/optical fiber bonded structural composite in a vibrationally isolated housing allowing an optical signal to be transmitted and detected from one optical fiber to another such that fluctuations of the surrounding magnetic field H will cause fluctuating mechanical torque on the bonded magnetostrictive beam which will be applied to the bonded cantilevered optical fiber to deflect or misalign and cause modulation of the said optical signal transmitted between the two fibers. This modulation can be calibrated to the dynamic variation of strength of a neighboring magnetic field to a precision of less than 1 fTe and sensitivity of 1 fTe/sqrtHz. The system is smart to selectively filter out any neighboring magnetic field with average strength smaller or greater than a certain critical value. The system is also smart enough to switch from one magnetic field average strength and/or direction to another with different average strength and/or direction.
Because of the high precision and sensitivity of the said magnetometer, its use in detecting weak magnetic fields emanating from biological tissues, organs, heart and brain presents a great potential for medical imaging.


A method and apparatus for removing plaque, fatty deposits, and other occlusions from blood vessels using ultrasonic energy. The method and apparatus has particular application in removing plaque from the carotid artery in a non-thermal manner. The apparatus is designed to have as small a cross-sectional profile as possible, therefore allowing the apparatus to be used in a minimally-invasive manner. As a result, the apparatus can be used in both surgical and outpatient treatment with minimal post-operative complications and minimal damage to areas other than the area of treatment. An ultrasonic probe may include aspiration channels on its outer surface. An aspiration sheath may surround the ultrasonic probe, such that the location of an aspiration port may be varied axially relative to the ultrasonic tip.

The invention relates to a method and an apparatus for removing plaque, including fatty deposits and other occlusions from blood vessels. More particularly, the invention relates to a method and apparatus for ablating plaque from the carotid artery by utilizing ultrasonic energy.
A blockage of a blood vessel is the most frequent cause of stroke and is responsible for about 75 percent of the nearly 150,000 U.S. stroke deaths each year. Stroke ranks as the third leading killer in the United States after heart disease and cancer. There are 500,000 to 600,000 new strokes in the United States each year. As many as 3 million Americans have survived a stroke with more than 2 million of them sustaining some permanent disability. The overall cost of stroke to the nation is $30 billion a year.
A carotid endarterectomy is a surgical procedure in which a doctor removes fatty deposits from one of the two main arteries in the neck supplying blood to the brain. Carotid artery problems become more common as people age. The disease process that causes the buildup of fat and other material on the artery walls is called atherosclerosis, commonly known as xe2x80x9chardening of the arteries.xe2x80x9d The fatty deposits are called plaque, and the resulting narrowing of the artery is called stenosis. The degree of stenosis is usually expressed as a percentage of the normal diameter of the opening. Carotid endarterectomies are performed to prevent stroke. Two large clinical trials supported by the National Institute of Neurological Disorders and Stroke (NINDS) have identified specific individuals for whom the surgery is highly beneficial when performed by surgeons and in institutions that can match the standards set in those studies. The surgery has been found highly beneficial for persons who have already had a stroke or experienced the warning signs of a stroke and have a severe stenosis of 70 percent to 99 percent. In this group, surgery reduces the estimated 2-year risk of stroke by more than 80 percent, from greater than 1 in 4 to less than 1 in 10. In a second trial, the procedure has also been found highly beneficial for persons who are symptom-free but have a severe stenosis of 60 percent to 99 percent. In this group, the surgery reduces the estimated 5-year risk of stroke by more than one-half, from about 1 in 10 to less than 1 in 20.
A stroke occurs when brain cells die because of decreased blood flow to the brain. In some cases, small pieces of plaque in the carotid artery may break loose and block an artery in the brain. The narrowed opening in the carotid artery can be a source of blood clots that travel to the brain, can trap blood clots from other areas of the body, or can become completely clogged.
U.S. Pat. No. 4,867,141 discloses a medical treatment apparatus which utilizes ultrasonic energy for medical treatment, particularly to break up a stone formed in a living body. An endoscopic channel is used to insert a portion of the apparatus into a body cavity, where an ultrasonic transmission member is used to transmit ultrasonic vibrations to the stone which is in contact with the distal end of the apparatus. A perfusion liquid is supplied to the area of the stone as the stone is being broken up by mechanical ultrasonic vibrations. This perfusion liquid is suctioned away from the area of the stone. As a result of the suction, the perfusion liquid and broken pieces of the stone are drained away from the body cavity. The apparatus of that patent is configured with an ultrasonic transmission member which is aligned and coaxial with the central axis of the probe, and therefore is effective in treating conditionsxe2x80x94such as stonesxe2x80x94where the irregularity or condition to be removed is aligned with the body vessel through which the endoscope passes. The device of that patent is used on non-hydrated calcified tissue, and uses direct mechanical vibration of the calcified tissue in order to result in tissue fracture and destruction.
U.S. Pat. No. 5,176,677 discloses an endoscopic ultrasonic rotary electro-cauterizing aspirator. The background section of that patent includes some discussion of medical literature relating to prostatectomies, and in particular the Krawitt et al. technique, in which a gland can be removed using ultrasonic treatment without effecting to the prostatic capsule. However, the apparatus shown in that patent is disclosed as being useful for arthroscopic surgery. The apparatus shown in that patent includes a feature for providing irrigating fluid to the tip of the ultrasonic probe, as well as mechanisms for aspirating the area around the tip. The aspiration and irrigation features of that invention require individual passageways coaxial with the ultrasonic working tip, each connected to a source of pressurized fluid, for irrigation, or to a source of reduced pressure, for aspiration. The apparatus of that invention also includes other features adjacent the tip, such as an insulated hood for removing obstructions, and a telescopic viewing apparatus. The irrigation, aspiration, insulated hood and telescopic viewing apparatuses all increase the cross-sectional profile of the apparatus. The design of that apparatus also is such that it may only treat areas which are directly axially in front of the ultrasonic probe, and therefore which are axially aligned with the lumen or incision through which the probe is inserted.
Various other patents show apparatuses which use ultrasonic energy to fragment or transform body tissue. U.S. Pat. Nos. 5,112,300; 5,180,363; 4,989,583; 4,931,047; and 3,805,787 each show ultrasonic treatment apparatuses for use in treating various medical conditions. In each of these patents, some mechanism is shown for providing irrigation and/or aspiration in the area where the ultrasonic treatment is being performed. In each of these patents, however, the mechanisms for irrigation or aspiration are structured such that they increase the overall cross-sectional profile of the instrument. In addition, in each of those patents, the irrigation and aspiration ports are a fixed distance from one another, which may not be varied.
xe2x80x9cUltrasonic processing,xe2x80x9d as used in the prior art for, inter alia, orthopaedic surgery, is a technique wherein a bodyxe2x80x94either liquid or solidxe2x80x94is, in effect, xe2x80x9cblastedxe2x80x9d by ultrasonic energy. In ultrasonic processing, the ultrasonic energy produced by the ultrasonic vibrator influences water molecules found within the body tissue. The ultrasonic energy is in the form of very intense sound vibrations at a very high frequency. These intense, high-frequency sound vibrations result in powerful chemical and physical reactions in the water molecules within the body tissue. The reactions in the water molecules ultimately results in a process called xe2x80x9ccavitation,xe2x80x9d which can be thought of as a form of cold (i.e., non-thermal) boiling of the water in the body tissue, wherein there is a rapid creation and collapse of numerous microscopic bubbles in the water.
The result of cavitation in water is a xe2x80x9cbreakingxe2x80x9d of that fluid. The rapid vibrations in water caused by the application of ultrasonic energy to the water and the resultant cavitation can cause fatigue in the water molecules which will break bonds between the water molecules. The result is that the water changes from a liquid form into a gaseous form, i.e., converts into steam, but this conversion is done without the need for application of thermal energy to the water. The result is a xe2x80x9ccold boilingxe2x80x9d of the water.
When a steam bubble is created in a cold liquid, such as upon the application of ultrasonic energy to water, the steam will condense because it is surrounded by a cold liquid. As a result, a void or cavity is created. The surrounding water molecules rush in to fill that cavity; when they reach the center of the cavity, they collide with each other with great force. This process is called cavitation. Cavitation is a known phenomenon which results in shock waves running outward from the collapsed bubble. The shock waves caused by cavitation can wear away or destroy material. For example, such shock waves are known to wear away metal at the edges of an outboard motor propeller.
Ultrasonic processing or ultrasonics is the application of sound at extremely high intensity and high frequency (normally above human hearing; 20 kHz and above) so as to result in material changes. Ultrasonics are used in a number of different applications in order to change a variety of different materials. Ultrasonics accelerates both physical and chemical reactions in the materials to which ultrasonic energy is applied and these reactions, among many other things, are accomplished largely due to the action of cavitation. There are more actions inherent in bubble collapse which are of significance. As used herein, the term xe2x80x9cbubblexe2x80x9d refers to a space within a liquid which contains a gas or vapor. However, after that gas or vapor condenses, there is still a void or cavity in that space until an implosion occurs. Therefore the term xe2x80x9cbubble,xe2x80x9d as used herein, also refers to the void or cavity.
One description of the manner in which cavitation is used in medical applications has been provided by Professor Lawrence Crum of the Applied Physics Laboratory at the University of Washington in Seattle, and can be found at the website: less than http://nero.apl.washington.edu/harlett2/artgwww/acoustic/medical/medical.html greater than . Professor Crum, writing about lithotriptryxe2x80x94in which a kidney stone is broken with ultrasonic energyxe2x80x94has stated that xe2x80x9c[w]hen pressure surrounding a bubble falls below the vapor pressure of the liquid, the bubble fills with vapor and grows explosively. The bubble collapses violently when pressure returns. If the collapse occurs near a boundary, such as [a] targeted kidney stone, a high velocity liquid jet is formed that impacts the boundary with great force. These extremely violent processes are thought to play a major role in stone destruction and associated tissue damage.xe2x80x9d
In addition to erosion or ablation of surfaces by the jet, cavitation causes many other actions. Notable among these in a purely physical sense is the action of intense shock fronts generated by imploding cavitation bubbles against kidney stones (lithotriptry), gall stones, tumors, and other intrusions in the body. Some of this action can also be accomplished by direct impact of a vibrating ultrasonic tool tip, but no (or minimal) cavitation is involved.
It is an object of the invention to provide a method and an apparatus for removing plaque, fatty deposits and other occlusions from the inner lining of blood vessels, particularly the carotid artery, using ultrasonic energy.
It is another object of the invention to provide an ultrasonic medical device capable of destroying and emulsifying plaque, fatty deposits and other occlusions, which can develop along the wall of the carotid artery, through cavitation with a high efficiency by means of a flexible probe operating in a transverse mode. As used herein, a transverse mode of operation is used to describe a flexible probe with a plurality of nodes and anti-nodes along the length of the probe.
It is a further object of the invention to provide a method and apparatus for removing plaque buildup from arterial walls which does not require direct contact with the wall and thereby avoids any potential damage to the artery.
The apparatus of the present invention is designed to have a small cross-sectional profile, therefore allowing the apparatus to be used in a minimally-invasive manner, either through the use and application of a small surgical cut down procedure to expose the artery or through the insertion of a small vascular introducer and the subsequent insertion of an ultrasonic probe to apply the energy source. In particular, the device according to the present invention may operate to remove deposits in the carotid artery from the internal lumen of the vessel outwards without necessarily requiring touching or direct abrasion of the vessel walls of the artery, which might otherwise be necessary with conventional methods and which can lead to damage of the artery walls. The application of the ultrasonic energy is applied in the lumen, wherein the energy migrates from the probe outward towards the obstruction or luminal constriction. Thus the microfragmentation of the materials occurs in a controlled fashion. On the other hand, traditional means of Carotid surgery typically requires the peeling of the occlusive materials from that of the vessel wall. This maximum contact fashionxe2x80x94where the plaque is xe2x80x9ctornxe2x80x9d from the vesselxe2x80x94causes secondary damage to the vessel. The present invention is advantageous in that it can be used in both traditional surgical sites and out-patient treatment with minimal post-operative complications and minimal damage to areas other than the area of treatment. The present invention therefore provides distinct advantages over the prior art in the treatment, and therefore provides an improved method of removing plaque from the carotid artery. It is to be understood, however, that although the present invention is designed for removing plaque from the carotid artery, its small cross-sectional profile makes it useful for treatment of any condition wherein minimally invasive techniques are advantageous and reduce post-surgical complications, and the present invention is therefore not limited to the treatment of removing plaque from the carotid artery. For example, the removal of plaque, fatty deposits and other occlusions in other blood vessels is possible using the invention.
The probe of the present invention is specifically designed to have a minimal cross-section, particularly for use for removing plaque from the carotid artery, thereby minimizing post-procedure complications and discomfort to the patient because larger sizes are more difficult to insert and uncomfortable. One way in which the present invention allows the cross-sectional profile of the probe to be minimized is by allowing aspiration to occur through grooves or channels on the outer surface of the probe. In this way, there is no need for an additional tubular aspiration sheath to be inserted into the carotid artery, to thereby provide a aspirating path.
The device is capable of reducing materials to levels equal to or smaller than 10 microns. With regard to remaining in the blood stream, it is known that particulate material of this size does not pose any health concerns. There are several ways to accomplish aspiration. For instance, a series of grooves or channels on the probe may be used. Instead, a standard vascular introducer can be used whereby aspiration is caused by the placement of an aspiration source on the luer lock fitting of the vascular introducer. In another embodiment, hollow tubes (as in a central lumen or an outer sheath that sits around the probe) can be used to draw and remove destroyed materials from the surgical site. This can be accomplished with a suction source at the handle or via the use of an induced aspiration through the ultrasonic motion of the probe or negative wave to pull the particulate back and out of the probe and surgical site. In each of these methods a relatively small amount of irrigation, e.g., approximately 10 ml per minute, may be provided to act as a lubricant to the site.
The terminus or termini of the irrigation passage can be located at the tip of the probe. Alternatively, the terminus or termini can be lateral to the probe tipxe2x80x94determined by the frequency of the system and the location of the nodes and anti nodes.
An object of the present invention is to provide a device and method for removing plaque from a vessel that is non-thermal. This is accomplished by the application of transverse ultrasonic energy which is extremely efficient, requiring substantially less energy to be delivered to the probe to stimulate cavitation. As a result of the reduced energy required, less actual losses in energy are realized during operation. Accordingly, because of the use of cavitation as the mechanism for destroying and emulsifying plaque, together with the use of irrigation and aspiration, the method and apparatus of the present invention can destroy and remove plaque within a range of temperatures of xc2x13xc2x0 C. from normal body temperature. Studies now show that this temperature range can be reduced even further. Therefore, complications attendant with the use of thermal destruction or necrosis of tissuexe2x80x94such as swelling or edemaxe2x80x94as well as loss of elasticity are avoided.
Various means to remove plaque from blood vessels are known in the art. For instance, carotid surgery can be accomplished by making an incision through a patient""s skin to expose the vessel, cross clamping the vessel to preclude flow, making an incision to open the vessel itself, removal of the occlusion, and closure of the vessel and the skin. Additionally, in a similar procedure, a bypass line can be used to allow for the small flow of blood to the brain during the procedure prior to the cross clamping and cessation of flow.
It is an object of the invention to provide a means to remove plaque from blood vessels without precluding blood flow. This is accomplished by avoiding contact with the arterial wall by inserting the probe into the vesselxe2x80x94like that of a standard vascular introducer stick. The probe sits in the vesselxe2x80x94in the middle of the lumenxe2x80x94surrounded by the occlusive materials.
The probe of the present invention, because of its significantly reduced cross-sectional profile, can be made to be flexible or bendable. The probe can be of a cross-section sufficiently small that the material of the probe is bendable through a wide range of articulation angles. The probe may housed in an articulated catheter or sheath, which catheter or sheath can be fabricated to be bendable or articulated. As a result, the present invention can be adapted to allow for the probe to activate and treat even areas of the body which are not axially aligned with the channel or lumen through which the probe is inserted. The articulation of the probe of the present invention allows for a xe2x80x9cwindshield wiperxe2x80x9d action of the probe tip, thereby creating a cone or arc sweep, greatly increasing the area of effect of the treatment through an incision.
The probe of the present invention is particularly useful in a treatment technique in which the treated area may be imaged by ultrasound imaging, in particular color ultrasound. The vibrating length of the probe echogenically produces a pronounced and bright image on ultrasound, and therefore is readily viewable by the surgeon or physician, greatly increasing the ease of use and effectiveness of treatment.
The probe of the present invention is particularly amenable, because of its small size, to the use of a flexible fiberoptic viewing device. The device preferably includes a fiberoptic cable tip which is fed with the probexe2x80x94either attached to the probe or separate from the probexe2x80x94and which cable is connected to a fiberoptic viewing eyepiece which is not connected to the handle or other equipment of the ultrasonic mechanism. In this way, manipulation of the viewing system is reduced to a minimum. The fiberoptic cable preferably includes a central optical viewing cable surrounded by illumination fibers. The fiberoptic cable may be located inside of a flexible sheath portion of the device, located on top of the flexible sheath, or may be located on top of a rigid sheath of the device.
The method of the present invention, because it uses ultrasonic energy prevents damage to the surrounding artery during insertion, treatment and removal, and also reduces or eliminates tissue damage, irritation and swelling in the patient.
The present invention also provides advantages to the physician rendering the treatment. The present invention is safer for the physician, because the components of the apparatus and method of the present invention deliver only ultrasonic energy, and as a result the ultrasonic energy""s affect is based on tissue planes and their hydration levels. Furthermore, the area in which the cavitation is effective in the apparatus of the present invention is an area on the order of 1-2 mm around the ultrasonic probe. As a result, the present invention allows a much higher degree of control of the affected area than prior art techniques. The present invention results in the destruction of no carotid artery wall tissue.
Another advantage of the present invention relates to the size of the particulate material broken down from the plaque. In all other applications used to remove occlusive materials, the operator is required to be vigilant in removing large particulate within the blood stream. This is because particulate larger than 500 microns may have significance to the patients overall health. However, in the present method, the application of ultrasonic energy towards the controlled destruction and removal of plaque results in particulate on the order of 10 microns or less. Thus, unlike with previously known methods, there does not appear to be a need for the down stream filters.
Traditional methods for removal of materials and exudate is through the use an aspiration mechanism which provides suction through a suction passage which is part of the probe. These traditional methods use irrigation fluid flow that is injected into the site where the procedure is being conducted, in conjunction with aspiration to remove the tissue from the surgical site. As discussed above, however, providing both irrigation and aspiration to the surgical site has, in prior art apparatuses, resulted in a probe of relatively large cross-sectional profile, and therefore that the treatment apparatus be substantially larger than the ultrasonic probe needed for conducting the procedure. These prior art apparatuses used concentric tubes wherein the irrigant is normally provide through a central core of the probe and the aspirant is provided an outer concentric tube and lumen.
Prior art apparatuses also maintain a strict orientation of the suction and the irrigation mechanism, such that the inner and outer lumens for irrigation and aspiration remain in a fixed position relative to one another, generally in a position closely adjacent the area of treatment. Additionally, if the probe is turned into an aspiration system, a problem arises in that the only location for fluid flow is at the tip of the probe, As a result, all the pressure (suction force) is focused there at this point within the vascular tree. Because of the tortuous nature of the vessels, single point suction tends to either clog or cause minor damage to the vessel.
One of the means of irrigation and aspiration in the present invention is to drill small holes or fenestrations along the length of the probe. Such fenestration are strategically placed at specific points of minimal stress due to the transverse cavitation. The use of fenestrations provides additional benefits. For example, in irrigation mode there is less of a focal pressure point out of which fluid is blown. Instead, fenestratrations allow for relatively diffuse irrigation along and around a length of the probe. Similarly, as for aspiration, by allowing suction to occur along the length of the probe, the suction pattern is greater. Among other possible benefits, this helps to prevent damage to the vessel wall and results in relatively more complete aspiration because of the larger suction pattern.
Thus, the irrigation lumen does not extend beyond the suction lumen (i.e., there is no movement of the lumens relative to one another) and the suction is designed to pick up any fluid and/or tissue remnants within the defined distance between the two lumens. The present invention, which uses grooves or channels on the outside of the probe for aspiration, or very small diameter hollow probes (xcx9c30 micron ID) allows for the distance between the irrigation and aspiration lumens to be varied, thereby allowing a reduced cross-sectional profile of the instrument inserted in to the patient""s body. In the present invention, an axially movable aspirating catheter or sheath may move along the length of the probe, to thereby vary the position of the aspiration lumen relative to the probe tip and the irrigation lumen or lumens. Central aspiration within hollow probesxe2x80x94especially those that are xcx9c0.020 in. diameter or smallerxe2x80x94allows for a flexible probe as well. This allows for the aspiration lumen, and the associated aspiration structurexe2x80x94except for the grooves or channels on the probexe2x80x94to be located outside the patient""s body.
In the application of the ultrasonic energy of the present invention the probe diameter is substantially smaller than that of traditional ultrasonic probes, and therefore is ideally designed for minimally invasive procedures. The present invention therefore relates to the application of small diameter probes, which can be inserted into a small diameter body vessel to thereafter use a cavitational effect to remove plaque. In order to increase the area of treatment which is effective in the small probe of the present invention, the irrigation lumens can be transverse to the axis of the probe, i.e., can open on the sides of the probe body. In this way, the maximum area of the probe tip is used to provide ultrasonic treatment and cavitational energy.
The probes used with the present invention are shaped to allow easy insertion, and so that they are not sharp so as to present the risk of tissue damage during insertion. The probes preferably include a taper that accommodates the insertion of the probe into the tissue through the application of the ultrasonic energy, wherein the energy is amplified through the transition from a larger mass to a smaller mass. The tapered shape of the probe, usually that of a cone, sphere, or hemisphere, ovoid tear drop shape is particularly useful in surgical applications as the tissue rent or tear caused by the insertion of the probe into the vessel is usually caused via a mechanical action of a needle or other sharp object, and not usually as a result of ultrasonic drilling of the probe. Irrespective, as the energy deposited by the probe is very low, and the round shape of the probe tip is formed, there is no additional energy departed upon the vessel to cause it to tear or that would otherwise cause a tear to expand beyond that of the initial penetration point.
Similarly, the tapered shape of the probe minimizes the overall size of the penetration point through the tissue, as the ultrasonic energy is focused at the extreme length of the flexible portion of the probe. The energy emanates for a defined length along this portion of the probe, and diminishes in transverse amplitude once specific transition barriers and shapes have been induced into the design.
In accordance with a preferred embodiment of the invention, an ultrasonic medical device comprises an ultrasonic vibration generator that generates vibration along its longitudinal axis. The ultrasonic vibration is transmitted through an ultrasonic coupler and a series of transformer sections that amplify the ultrasonic vibration. A flexible member is coupled to the distal end of the transformer sections, and is thus supplied with a longitudinal vibration at its base by the transformer sections. The flexible member is designed so that it converts the longitudinal vibration into a standing wave that runs along the length of the flexible member. The standing wave produces a series of nodes and anti-nodes along the length of the flexible member. Each of the anti-nodes produces cavitation in fluids in contact with the probe. The cavitation of the fluids causes destruction of adjacent plaque. Thus, in this manner, the entire length of the flexible member becomes a working surface that may be utilized for destroying plaque.
The invention, therefore, includes a number of advantageous features which make it particularly useful for minimally-invasive procedures. First, it allows for the application of ultrasonic energy to plaque, such as that which lines the carotid artery, via a small diameter probe that is able to traverse a vessel or opening, and which can remove plaque through the action of cavitation on the plaque. Second, the invention has the ability to make a small penetration into and through a body vessel, or to create a small penetration in the body, and thereafter allows the probe to be directed to the blood vessel to be treated, such as the carotid artery. Third, the invention allows, through the action of cavitation and a movement by the surgeon of the ultrasonic tip throughout the treated area, the creation of a large cavity, so that the cavity is larger than the size of the probe. Fourth, the apparatus of the invention may be designed with a stiffened outer member, within which a softer malleable or bendable member resides, which therefore allows the ability to insert a probe into the body, without extreme torsion and bending on the anatomy. This malleability also allows the probe to be bent or articulated so that it can reach areas which are not axially aligned with the lumen or passage into which the probe is inserted. Fifth, the invention allows the ability to remove debris at the point of the procedure. Sixth, the present invention allows the ability to irrigate the cavitation site via the ultrasonic probexe2x80x94both when the probe is rigid and when the probe is flexible and malleable. Seventh, the present invention allows the use of ultrasonic energy which is applied to plaque and fatty deposits selectivity, because it uses energy in a frequency rangexe2x80x9420 kHz to 80 kHzxe2x80x94such that it imparts the energy specifically to hydrated (water-laden) plaque and fatty deposits. As a result, there is little or no energy imparted to the arterial wall itself. This selectivity in the application of energy therefore avoids damage to the artery. Eighth, the present invention allows the use of bending, flexing or articulated probe, which limits the amount of force placed upon the probe as it is advanced forwards. In this way, the force applied on the probe is decreased through the bend, i.e., less pressure is imparted on the tip of the probe, thereby decreasing the potential for accidental penetration of tissue by the probe through pure physical force. That disadvantageous result might have occurred in a similar application of force using a straight probe into the prostatic capsule.
An important feature of the present invention is that it is non-thermal. The use of a procedure in which heat or thermal energy is not used is important, and the present invention produces very low heat, and the excursion of heat is limited to the immediate area associated with the acoustic wave that is ablating the plaque. The present invention, through the use of ultrasonic energy together with irrigation and aspiration, can produce treatment within a range of normal body temperature in the treated area of xc2x13xc2x0 C. Furthermore, collateral irrigation causes the residual tissue to remain within a narrow range around normal physiologic temperatures throughout the procedure of the present invention. Due to the lack of heat in the present invention, and the immediacy of the plaque removal process, the residual tissue exhibits remarkably little to no inflammatory response, thereby producing little fibro intimal hyperplasia edema (swelling) of the vessel. As such, loss of vessel patency or vessel internal diameter is avoided.
The ultrasonic tip of the present invention, because it uses cavitation as the mode of plaque removal, does not have to be sharp. Rather, soft flexible shapes are preferred because penetration is caused by a mechanical penetration of the vessel not cavitation, and not by the physical shape of the probe. Therefore, the tip can be smooth and small, making insertion less traumatic and less prone to residual tissue damage.
In the present invention, the location of the probe can be determined via the use of a medical visual ultrasound device. Once the probe is located, the bending or flexure of the probe tip can be monitored. This enhances the physician""s ability to see and direct the ultrasonic probe during treatment, and is the result of the high frequency vibrations at the tip.
The ultrasonic energy to be applied to a particular treatment site is a function of the amplitude and frequency. In general, the throw rate or amplitude of the energy supplied by the apparatus of the present invention is in the range of 150 microns to 350 microns, and the frequency in the range of 20-80 kHz. Larger probes will use the lower frequencies while smaller probes will use the higher frequencies.

Apparatus for removing plaque from blood vessels using ultrasonic energy